The goal of the current proposal is to evaluate the hypothesis that traumatic brain injury alters intercellular communication between astrocytes, a potentially crucial and often overlooked aspect of brain processing. Astrocytes were once viewed as passive cells, but are now characterized as active contributors to signal processing in the brain. Yet, the effect of traumatic injury on calcium-mediated astrocyte intercellular signaling has not been evaluated. Therefore, the proposal evaluates the hypothesis that traumatic injury alters intercellular calcium signaling between astrocytes in the glial syncytium using the following specific aims: Specific Aim 1: Injury of cortical astrocytes alters origination and propagation of intercellular calcium waves. We will compare the velocity and distance of intercellular calcium waves in injured astrocytes to that of uninjured astrocytes. (Method: Use quantitative fluorescent microscopy to evaluate intercellular calcium waves). Specific Aim 2: Injury alters gap junction coupling. We will compare fluorescent dye transfer through gap junctions, expression of Connexin 43 protein, and phosphorylation of Connexin 43 protein between uninjured and injured astrocytes. (Method: Use lucifer yellow transfer to measure coupling of gap junctions; use Western Blots to measure expression and phosphorylation of Connexin 43 protein). Specific Aim 3: Intercellular calcium signaling will be maintained in astrocytes by pharmacological manipulation of IP3-mediated intracellular calcium signaling. (Method: Use agonists and antagonists of elements in the signaling pathway to determine if alterations in intercellular calcium waves can be attenuated). These proposed experiments evaluate, for the first time, the effect of traumatic brain injury on the intricate and extensive calcium signaling network among astrocytes. Aim #1 directly examines the effects of mechanical injury on intercellular calcium signaling in astrocytes. Aim #2 examines the potential mechanisms (i.e. gap junctions) involved in injury-induced alterations in intercellular calcium signaling. Aim #3 examines potential therapeutic interventions which could restore intercellular signaling. The results of the proposed experiments may provide not only new insights into the pathophysiology of TBI, but also potentially lead to the development of novel therapeutic approaches for the treatment of the traumatically injured brain.